Torsion predamping device

ABSTRACT

A torsional pre-damping device for damping the impact between a hub and a hub disc. A crown insert (20) made of absorbent material is arranged between the engaging teeth (18) and the engaged teeth (19) of the loose meshing portions (16) defined between the disc and the hub.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to a torsion predamping device comprisingat least two coaxial parts, mounted rotationally in relation to oneanother within the limits of a determined angular clearance andassociated with resilient predamping and centring means.

The present invention more particularly relates to an improvement to apredamping sub-assembly intended to dampen the impact of the shockbetween a hub and a hub disc at the end of their angular clearance.

b) Description of Related Art

In a known torsion damping device, one of the rotational parts bears adriven plate assembly intended to be rotationally connected with a firstshaft, in practice a driving shaft, the crankshaft of the internalcombustion engine in the case of an application to a motor vehicle,whereas another of the rotational part comprises a hub by which it isintended to be rotationally connected with a second shaft, in practice adriven shaft, the primary shaft of a gearbox in the case concerned ofsuch a motor vehicle.

In such an assembly, from document FR-A-2 496 210 it is known forexample to add a torsion predamping sub-assembly in which thedelimitation of the angular clearance between the two coaxial parts isprovided by loose meshing means provided with small studs, made ofelastomer, placed on the loose meshing teeth of one of the coaxialparts, against which the loose meshing elements of the other coaxialpart come to abut in order to reduce the noise of impact at the end oftravel of the loose meshing means.

However this solution does have drawbacks. On account of their reducedsize, the studs indeed only provide localised damping, resulting in aresidual noise which can not be eliminated. Moreover, the service lifeof these elastomeric elements is limited and they weaken the teeth onwhich they are placed.

SUMMARY OF THE INVENTION

To reduce these difficulties, the present invention proposes a newtorsion predamping device, especially for a motor vehicle clutch,comprising two coaxial parts with loose meshing means between them andmounted rotationally in relation to one another in opposition toresilient means called predamping and centring means, characterised inthat the meshing means comprise engaging teeth and engaged teeth and acrown insert made of material absorbing the shocks is disposed betweenthe teeth.

All the moment of torsion is transmitted by means of the crown insert.The latter is relatively cheap to manufacture and is simple to put inplace.

Furthermore, the loose meshing means (the engaging and engaged teeth)are not weakened, in contrast to those in document FR-A-2 496 210.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will moreoverbecome apparent from the following description, by way of example, withreference to the drawings on which:

FIG. 1 is a sectional view of a clutch friction with a predamping deviceaccording to the invention;

FIG. 2 is a detailed view of the box of FIG. 1 on a larger scale;

FIG. 3 is a sectional view of FIG. 2, along line III--III;

FIG. 4 is a similar view to that of FIG. 3 according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

These figures illustrate by way of example the application of theinvention to a torsion damping device, which, intended to form a clutchfriction for a motor vehicle clutch, comprises, successively rotatinglymounted two by two in relation to one another, three coaxial parts, i.e.a part A, essentially formed by a hub 10, a part B, essentially formedby a hub disc 11, which surrounds the hub 10, and a part C, essentiallyformed by two guide washers 12, disposed on either side of the hub disc11 and surrounding the hub 10, connected to one another by small posts 9and therefore actuated by the same rotational movement.

The coaxial part C bears a driven plate assembly 13, the frictionlinings of which are intended, in a known manner, to be clamped betweentwo plates rotationally connected to a driving shaft, the third motionshaft at the crankshaft of the engine in the case of a motor vehicle.

The hub 10 itself has internal splines 14, intended to connect it forrotation to a driven shaft, the primary shaft of associated the gear boxin the case of such a motor vehicle.

The coaxial parts B and C are rotationally mounted in relation to oneanother, in opposition to resilient means interposed circumferentiallybetween them, formed, in the represented embodiment, by springs 15 and15a of the coil spring type mounted, in a known manner, in openings madefacing one another in the guide washers 12 and in the hub disc 11. Theassembly thus formed-by the coaxial parts B, C and the springs 15, 15aforms the main damping device for the clutch friction. Its operation,well known in its own right, will not be described in further detail andis not dependent on the present invention.

The coaxial parts A and B are also mounted rotationally in relation toone another, in opposition to resilient predamping and centring means,within the limits of an angular clearance determined by loose meshingmeans 16 defined between the disc 11 and the hub 10.

In practice, on its outer periphery, on a longitudinal portion 17 of itsouter face, the hub 10 has radial projections 18 forming engaging teeth.On its inner periphery, opposite the portion 17 of the hub 10, the hubdisc 11 itself has slots 19, having an angular opening larger than thatof the teeth 18, thus forming engaged teeth. A tooth 18 is engaged ineach slot 19, the possible angular clearance between the coaxial parts Aand B thus being limited by the teeth 18 of the hub 10 coming to abetwith the corresponding sides of the slots 19 of the disc 11. The teeth18 and slots 19 thus form the above-mentioned loose meshing means 16 andhave an overall trapezoidal shape.

The device is completed by a predamping sub-assembly comprising inparticular a predamping cassette of known type, disposed between the hub10 and the hub disc 11 within the limits of their angular clearance,determined by loose meshing means 16. This cassette is situated in aplane offset in relation to that of the hub disc 11, in the axialdirection. It is mounted axially between the disc 11 and one of theguide washers 12. It is formed by a secondary disc 40 fixed, here byclinching, with the hub 10, placed between flanges 26, themselvesrotationally connected to the hub disc 11 by fingers 41. The fingers 41are engaged in holes of the hub disc 11, with the result that theflanges 26, 26' are rotationally driven with the hub disc 11.Circumferentially acting springs 27 are connected between the flanges26, 26' on the one hand, and the secondary disc 40 on the other hand, inaccordance with a conventional arrangement, the flanges 26, 26' and thedisc 40 having facing one another holes for housing the springs 27.

The springs 27 are resiliently biased by a relative rotation of the hubdisc 11 and of the hub 10 and therefore act in opposition to such arotation, tending to bring the hub and the disc back into anintermediate position of their angular clearance (see FIG. 3). Afriction washer 22A may be sandwiched between the predamping cassetteand the hub disc 11. The operation of such a predamping cassette isknown.

As a reminder, it will be recalled that the springs 27 are less stiffthan the springs 15, 15a. In a first phase, the springs 27 arecompressed, the guide washers 12 and the hub disc 11 forming an assemblyby means of stiffer springs 15, 15a, this movement continuing until theclearance of the loose meshing means 16 has been removed. Afterwards,the springs 27 remain stretched and a relative movement is producedbetween the discs 11 and the guide washers 12 with the intervention ofthe springs 15, 15a.

It will be noted that the fingers 41 are derived from one of the flanges26 and each passes through a slot made on the outer periphery of theother flange 26'.

Each finger 41 has a spherical deformation at its end for mounting byclipping the flange 26 having fingers 41 on the other flange 26, bothflanges being metallic, after mounting the secondary disc 40 and thesprings 27.

According to an important characteristic of the invention, thepredamping sub-assembly also comprises an insert, in the form of acrown, made of shock-absorbent material, placed between the engagingteeth of the hub 10 and the engaged teeth of the hub disc 11.

According to a first embodiment, represented on FIG. 3, the insert ismade of shock-absorbent or noise-limiting material, for example ofplastics, lead, cast iron or aluminium, and has better dampingproperties than steel. It may then assume the shape of the engagingteeth, or according to a preferred embodiment, the engaged teeth. Whenthe insert 20 is placed against the teeth of the hub disc 11, it is laidflat and retained thereagainst by centrifugal force.

Excessive thicknesses may be provided on the contact faces of the insert20 with the teeth in order to increase the absorbent capacity of theinsert.

According to a second embodiment, represented on FIG. 4, the absorbentproperty of the insert 20' is essentially bestowed thereupon by itsconformation. Spaces 21 are provided between the insert 20' and thecontact faces of the engaging and engaged teeth, with the result thatthe insert does not totally cover any of the two sets of teeth.

Before reaching the end of travel, the teeth 18 come to crush the insert20' towards the sides of the slots 19, reducing the spaces 21. Theimpact of the teeth 18 at the end of travel against the slots 19 is thusdamped.

In all cases, the positioning of the insert will be facilitated if it isslit.

To avoid a displacement of the insert 20 along the axis around which thehub 10 and the hub disc 11 are situated, friction washers 22A and 22B,coaxial to the disc 11, may be advantageously disposed on either side ofthe insert 20. This insert is therefore retained axially between thesetwo washers.

According to a particular embodiment, the insert 20 may be attached toone of the friction washers, regardless of whether it is stuck onto thiswasher, or whether it is moulded.

As a variant, the predamping device may directly act between the disc 11and the hub 10 as described in the above-mentioned document FR-A-2 496210.

Of course, the insert may cover the engaging teeth. It may be stuck ormoulded onto the hub 10 or the disc.

The insert may have a variable thickness and have for example a greaterthickness at the level of its active shock-absorbing zones and lesserthickness at the level of its inactive zones.

On their inner periphery the friction washers 22A and 22B may haveengaged teeth to mesh with the engaging teeth of the hub 10 with lessclearance than that provided between the engaging teeth of the hub 10and the engaged teeth of the hub disc 11.

This contributes towards braking the movement between the parts B and Aat the end of the travel, the washers 22A, 22B being subject to theaction of a Belleville washer 1 bearing on the guide washer 12 notassociated with the driven plate assembly 13 for action on adistribution washer 2 connected rotationally by pins to the washer 12(FIG. 1) and clamping of the washers 22A and 22B with the contact of thedisc 11 and of the predamping cassette between the disc 11 and the otherwasher 12.

Of course, just one of the friction washer 22A, 22B may loosely meshwith the hub 10, the other being for example integral with thedistribution washer 2. The washers 22A, 22B may mesh with differentclearances with the hub 10, and even without any clearance. Allcombinations are possible.

We claim:
 1. A torsion predamping device comprising first and secondcoaxial parts (10, 11) with loose meshing means (16) between saidcoaxial parts rotatingly in relation to one another in opposition toresilient predamping means wherein said first coaxial part comprises ahub (10) having engaging teeth (18) on an outer periphery thereof, whilesaid second coaxial part comprises a hub disc (11) surrounding the hub(10), said hub disc (11) having engaged teeth (19) on an inner peripherythereof, engaged teeth (19), wherein said meshing means comprise saidengaging teeth (18), said engaged teeth (19) and a crown insert (20)made of shock-absorbent material radially disposed between said engagingand engaged teeth, and wherein the resilient predamping means are housedin a predamping cassette disposed between the hub (10) and the hub disc(11), said predamping cassette being disposed in a first plane offset inrelation to a second plane of said hub disc (11) said crown insertcomprising a single piece member substantially circumscribing a commonaxis of said coaxial parts and being axially disposed and retainedbetween two friction washers (22A, 22B) coaxial with said hub (10).
 2. Adevice according to claim 1, characterised in that the insert (20) isintegral with one of the adjacent friction washers (22A, 22B).
 3. Adevice according to claim 1, wherein the insert is moulded to one of thehub and the hub disc.
 4. A device according to claim 1, wherein theinsert (20) is moulded to one of the friction washers.
 5. The torsionpredamping device according to claim 1, wherein said crown insert (20)is placed against the engaged teeth of said hub disc (11) so as to belaid flat and retained thereagainst by centrifugal force therebysubstantially assuming a shape of the engaged teeth.